7th Grade Science Student ebook

12.2 HOW EARTH CHANGES

CHAPTER 12: EARTH AND LIFE HISTORY

Plate tectonics

What is plate

tectonics?

How the continents move is explained by a theory called plate

tectonics. Earth’s outer layers are called the lithosphere. The

theory of plate tectonics, first stated in 1965, refers to the

movement of giant pieces of the lithosphere called lithospheric

plates. The movement of one plate causes the pulling or pushing

of other plates, significantly affecting Earth’s surface. There are

seven large lithospheric plates and many smaller ones.

Movement of

tectonic plates

Forces beneath the lithosphere cause the plates to move. Some

plates include continents (Figure12.11). The continents move with

their plates. The plates that include North America and Europe are

moving apart at a rate of a little over 2 centimeters each year. By

comparison, your fingernails grow at a rate of 2.5 centimeters a

year. Though that rate may seem slow, it has produced enormous

changes in Earth’s surface over millions and millions of years.

Figure 12.11: The movement of

tectonic plates causes the continents to

move.

plate tectonics - a theory that

describes how the continents

move.

lithospheric plates - giant

pieces of solid rock on Earth’s

surface.